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This study presents interplanetary trajectory options for the Double Asteroid Redirection Test (DART) spacecraft to reach the near Earth object, Didymos binary system, during its 2022 Earth conjunction. DART represents a component of a joint NASA-ESA mission to study near Earth object kinetic impact deflection. The DART trajectory must satisfy mission objectives for arrival timing, geometry, and lighting while minimizing launch vehicle and spacecraft propellant requirements. Chemical propulsion trajectories are feasible from two candidate launch windows in late 2020 and 2021. The 2020 trajectories are highly perturbed by Earth's orbit, requiring post-launch deep space maneuvers to retarget the Didymos system. Within these windows, opportunities exist for flybys of additional near Earth objects: Orpheus in 2021 or 2007 YJ in 2022. A second impact attempt, in the event that the first impact is unsuccessful, can be added at the expense of a shorter launch window and increased (∼3x) spacecraft Δ V . However, the second impact arrival geometry has poor lighting, high Earth ranges, and would require additional degrees of freedom for solar panel and/or antenna gimbals. A low-thrust spacecraft configuration increases the trajectory flexibility. A solar electric propulsion spacecraft could be affordably launched as a secondary spacecraft in an Earth orbit and spiral out to target the requisite interplanetary departure condition. A sample solar electric trajectory was constructed from an Earth geostationary transfer using a representative 1.5 kW thruster. The trajectory requires 9 months to depart Earth's sphere of influence, after which its interplanetary trajectory includes a flyby of Orpheus and a second Didymos impact attempt. The solar electric spacecraft implementation would impose additional bus design constraints, including large solar arrays that could pose challenges for terminal guidance. On the basis of this study, there are many feasible options for DART to meet its mission design objectives and enable this unique kinetic impact experiment. [ABSTRACT FROM AUTHOR]

Abstract: Taking inspiration from the orbital dynamics of dust, we find that spacecraft length scaling is a means of enabling infinite-impulse orbits that require no feedback control. Our candidate spacecraft is a 25μm thick, 1cm square silicon chip equipped with signal transmitting circuitry. This design reduces the total mass to less than 7.5mg and enables the spacecraft bus itself to serve as a solar sail with characteristic acceleration on the order of 0.1mm/s2. It is passive in that it maneuvers with no closed-loop actuation of orbital or attitude states. The unforced dynamics that result from an insertion orbit and a launch-vehicle separation determine its subsequent state evolution. We have developed a system architecture that uses solar radiation torques to maintain a sun-pointing heading and can be fabricated with standard microfabrication processes. This architecture has potential applications in heliocentric, geocentric, and three-body orbits. [Copyright &y& Elsevier]

Mission engineers have detected an unexpected anomaly on six spacecraft during low-altitude gravity-assist maneuvers around Earth. This Earth flyby anomaly involves an acceleration that, to date, researchers cannot account for based on known forces or errors in measurement or modeling. This paper evaluates Lorentz accelerations associated with spacecraft electrostatic charging as a possible explanation for the Earth flyby anomaly, This analysis does not explicitly address plasma physics but, instead, bases its conclusions on fundamental six-state flight dynamics. The analysis focuses on the Near Earth Asteroid Rendezvous spacecraft, because it exhibited the largest anomalous error with the smallest estimated residuals. The analysis takes the form of a boundary-value problem in which vector-disturbance time histories are found numerically through nonlinear optimization methods. The analysis identifies the unknown, but required, acceleration based on a model of the Lorentz-force interaction. The algorithm cannot converge on a solution that fully reproduces the anomalous error in all six orbital states, It is unlikely, based on this analysis, that Lorentz forces cause the flyby anomaly. [ABSTRACT FROM AUTHOR]

It is challenging or infeasible to precisely measure the mass of small asteroids using the state-of-the-art without a dedicated spacecraft rendezvous mission, which are typically limited to one or a few asteroid targets. Alternatively, spacecraft flyby missions offer the possibility of visiting multiple asteroids but typically lack the sensitivity to measure mass for all but the largest asteroids. In these encounters, Earth-based two-way Doppler is used to measure a change in the spacecraft's velocity imparted by the asteroid. The technique known as Optical Gravimetry (OpGrav) seeks to increase this sensitivity of mass measurements from flyby encounters using optical measurements from the spacecraft to one or more test-masses. In this technique, the spacecraft deploys the test-masses prior to an asteroid flyby and then tracks them before and after the encounter using an on-board telescope. The test-masses can pass much closer to the asteroid than a spacecraft would typically choose such that their trajectories are measurably deflected. This paper provides a quantitative sensitivity analysis of the design parameters most relevant to OpGrav, including asteroid mass, flyby velocity, number of test-masses, test-mass target altitude, test-mass deployment time, and the cadence of optical measurements. Additionally, this paper investigates the effect of practical test-mass deployment errors on the expected mass measurement. Broadly speaking, this analysis shows that OpGrav provides comparable sensitivity to the existing technique at asteroids that are five to ten times smaller in diameter, depending on whether one or three test-masses are deployed. We demonstrate that under realistic mission assumptions, the use of OpGrav would have allowed all previous flyby visits of asteroids, most of which were not able to obtain mass estimates, to achieve better than 25% 1 σ accuracy in mass measurements, representing a significant improvement on the state of the art. • Optical tracking of test-masses greatly improves asteroid flyby mass estimation. • Can obtain mass estimates of asteroids as small as 500 ​m in diameter. • Can obtain mass estimates for flybys up to 20 ​km/s for bodies ≥ 1 ​km in diameter. • Tracking 3 test-masses is necessary for most sensitive measurements. • Optical gravimetry has minimal impact to other spacecraft science activities. [ABSTRACT FROM AUTHOR]